Study of structural and electrical properties of grain-boundary modified ZnO films prepared by sol–gel technique

ZnO films, prepared using sol–gel techniques, were extensively studied in order to elucidate the structural and electrical properties at low temperature. The grain size decreases with aluminum doping up to a certain extent as is evident from SEM micrographs. DTA, TGA, DTGA and FT-IR analysis have been done on the specimens. The present analysis supports the view of formation of zinc monoacetate as an intermediate product prior to the formation of zinc hydroxide. The hydroxide is reduced to oxide in presence of oxygen and assumes an ordered state around 425 °C. Aging effects on the electrical properties have been noted. The electrical conductivity increases and becomes almost constant after 3 months. The film shows optimum conductivity when annealed at 550 °C for sample doped with 1.7 at.% of Al. Possible Al segregation along the grain boundary obstructing further grain growth increases the resistivity with further doping. The temperature dependence of electrical conductivity between 200 and 300 K indicates carrier scattering by the potential barrier at the grain boundaries having a barrier height in the range of 40–90 meV. Below 200 K, the nature of curve suggests variable range hopping conduction. Mott’s parameters in the variable range hopping conduction have been estimated for the films.